1. Field of the Invention
The present invention relates to a communication system and a transmitter-receiver for use therewith, and more particularly to power control in an MIMO (Multiple Input Multiple Output) communication method.
2. Related Art
In a personal radio communication system, the higher communication rate has been achieved owing to the broadband. One of the techniques is a method called an MIMO (refer to Japanese Patent Laid-Open No. 2003-348057). In the MIMO communication method, each of a transmitter 1 and a receiver 2 is provided with a plurality of antennas, in which high speed data to be transmitted is divided into N and transmitted via respective antennas on the transmitter 1, and the transmitted data is restored by making a predetermined signal processing for the signals received by M (M≧N) antennas on the receiver 2, as shown in FIG. 3.
That is, in the transmitter 1, the data to be transmitted is divided into N by a data division part 11, and transmitted via N transmitting circuits 12-1 to 12-N from N antennas. In the receiver 2, the transmitted data is received via M antennas and receiving circuits 21-1 to 21-M, whereby data is restored by a data synthesis part 22.
The data is transmitted at N times the rate in a frequency band according to the speed of signal transmitted from each antenna. Since different signals transmitted from plural antennas in this way are added and received on the receiving side, the signals transmitted from respective antennas can not be directly separated. Therefore, plural antennas are prepared on the receiving side, whereby the signals are separated by analyzing plural signal rows received through different transmission channels.
As an application example of this MIMO communication method, the MIMO communication may be implemented by connecting plural communication apparatuses that do not make the MIMO communication in the normal mode, as disclosed in Japanese Patent Laid-Open No. 2003-332963. In FIG. 4, the transmitters 1-1 to 1-N and receivers 2-1 to 2-M are independent of each other in the normal mode, but in making the MIMO communication, the MIMO communication apparatus is made by connecting plural transmitters and receivers.
The transmission data inputted into the transmitter 1-1 is firstly divided by the data division part 11, one of the data being transmitted from an antenna via a transmitting circuit 12, and the other being outputted to the transmitter 1-2. In the transmitter 1-2, the data from the transmitter 1-1 is also divided, one of the data being transmitted from an antenna, and the other being outputted to the transmitter 1-3. In this way, the transmission data is divided and transmitted from N transmitters, whereby the data of N times the transmitting capability in the normal mode can be transmitted.
On the receiving side, data received in a receiving circuit 21 of each of the receivers 2-1 to 2-M is synthesized by a data synthesis part 22, and decoded in accordance with an MIMO receiving algorithm. In this way, the signals from the transmitters 1-1 to 1-N are received by M receivers, whereby the high speed reception is achieved by the MIMO communication method.
In the case where the MIMO conFIGuration as described above is not taken, it is common that the transmitter power of the transmitting side is controlled in accordance with a feedback signal from the receiving side, as shown FIG. 5. That is, in the receiver 2, a power control signal is generated from a received signal of the receiving circuit 21 by a power control signal generation part 23, and transmitted via a transmitting circuit 24. In the transmitter 1, this power control signal is received by a receiving circuit 13 and a power control signal extraction part 14, whereby the transmitter power of the transmitting circuit 12 is controlled based on the received power control signal.
If such a general transmitter power control method is directly applied to the MIMO conFIGuration, the power control signal is generated based on the reception power in each receiver, independently, whereby there is a drawback that the optimal transmitter power can be made as the entire system.